The invention concerns an optoelectronic sensing device for the contactless detection of contrasting marks (also referred to as “contrast marks”).
For simple tasks, such optoelectronic sensing devices are known as one-track systems for identification of contrast marks.
For more complex tasks, however, contrast marks must be arranged on two adjacent reading tracks.
With the contactless detection or identification of such contrast marks, it is possible to obtain the most diverse information concerning the carrier material for the marks. Depending on the shape, geometry and/or color of the marks, for example, one can determine the exact position, the speed and/or the direction of movement of the carrier material for the marks.
Contrast marks are used, for example, to control multicolor printing machines, in which individual partial color images must be precisely aligned on top of each other. In such an application, the exact orientation is attained by printing a first contrast mark along with the first partial color image. Additional contrast marks are printed with the subsequent partial color image, so that the contrast marks that are to be compared will be situated next to each other along two reading tracks. By optoelectronically sensing the carrier material, the position and movement direction of the first printed contrast mark are then compared with the subsequently printed contrast marks. If a shift in the position of these contrast marks is observed, the phase position of the individual printing cylinder is adjusted, for example with suitable servomechanisms, so that the contrast marks and therewith also the individual partial color images are positioned with respect to each other within a permitted tolerance range.
Another application for such optoelectronic sensing devices is in the area of industrial packaging, which encompasses, for example, the simple packaging of foodstuffs as well as the production (printing, cutting out, punching, folding) of high-quality packaging materials. In order to automate these processes, knowledge of the exact position of the packaging material in the processing machinery is required. Contrast marks applied to the packaging material are used for retrieving the needed information.
A further field for the application of optoelectronic sensing devices is in the field of modern transport and conveying equipment and logistics for the handling of goods of all kinds. For such systems, identifying the instantaneous position of an object is often not sufficient and other information such as, for example, a characteristic of the object or its further transportation path may be needed.
Optoelectronic sensing devices are known which can accomplish a contactless detection of contrasting marks arranged next to each other along two reading tracks on a moving web. In these known arrangements, one or two light sources and at least two light receivers are located in a common housing. Behind a common light exit opening in the common housing are two lenses which direct the emerging light onto the contrasting marks. Light is reflected by the marks, or the carrier material for the marks is then directed back to the associated light receiver. Such known optoelectronic sensing devices for two-track systems have two light sensing inserts, which are installed in a common housing in a fixed and unvariable relationship with respect to each other.
It is likewise known to mount two individual self-contained one-track light sensors next to each other and to process the two individual output signals in a common evaluating circuit so as to form composite information from the contrast marks on two reading tracks.
A drawback with the prior art is that when the two light sensing systems are fixedly arranged in a common housing, the distance between the two reading tracks is also fixed and invariable. This limits the possible configurations the contrast marks may take and/or the carrier material for these contrast marks may have.
The solution employing two individual self-contained light sensors in two separate housings that are adjustable to conform to the track spacing has the drawback that it requires a minimum track spacing because the two individual housings are relatively large. The area occupied by the contrast marks must be large. This is particularly troublesome because, in addition to the contrast marks, other symbols or representations are typically present on the carrier material, which can result in an undesirably large information density on the carrier material.
Thus, there is a need for an optoelectronic sensing device for detecting contrast marks on two adjacent reading tracks which is easily adapted for use with different reading track spacings. Such sensing devices should be dimensioned such that even very small track spacings can be accommodated.